The other day I was having lunch at one of the Asian-fusion restaurants in Zürich with a (non-Asian) friend. At one point, he speared a piece of chicken with one chopstick, brought it to his mouth and pried it off with his teeth. I must have a strange expression on my face, because he looked at me and asked me what was wrong.

Of course he did not know that in Japan, what he just did would be considered to be terribly rude, in the same way that someone who didn't grow up in Europe might not know about not putting your elbows on the table. I explained this to him, and he sort of snorted and said "well why don't you write a guide to chopstick manners on your site then!"